Blister



FIG. 1 is a left, front, top perspective view of a blister;

FIG. 2 is a front elevational view thereof; and,

FIG. 3 is a top view of the blister of FIG. 1.

The back elevational view is plain and unornamented forms no part of the claimed design.

The broken lines shown in the drawing disclosure are for illustrative purposes only and form no part of the claimed design. 

We claim the ornamental design for a blister, as shown and described. 